1. Field of the Invention
The present invention relates to a micromechanical sensor device and a method for manufacturing a micromechanical sensor device.
2. Description of the Related Art
Micromechanical sensors for measuring, for example, acceleration and rotation rate, are known, and are mass-produced for various applications in the automotive and consumer sectors. MEMS elements, which are manufactured using surface micromechanical methods, are known in particular. Here multiple oxide and polycrystalline silicon layers are deposited on a silicon substrate and patterned. The MEMS wafer is then hermetically sealed with a cap wafer.
FIG. 1 is a cross-sectional view of a conventional surface micromechanical sensor. In this example a MEMS wafer 100 encompasses three functional layers in the form of polysilicon layers 10, 20, 30 that can be patterned largely independently of one another. Oxide layers 11, 21 located respectively between them can be opened at specific sites so that through contacts between polysilicon layers 10, 20, 30 can be implemented. First polysilicon layer 10 functions preferably as an electrical wiring plane; second polysilicon layer 20 and third polysilicon layer 30 can be used both for wiring and in order to implement movable MEMS structures. The MEMS structures are released, for example, by controlled removal of oxide layers 11, 21 beneath polysilicon layers 10, 20, 30 by etching with gaseous HF.
The MEMS element, for example an acceleration or rotation rate sensor, possesses at least one mechanical mount 33, at least one spring assemblage 31, and movable mass elements and electrode elements 22, 32 that, in the example of FIG. 1, are implemented both in second polysilicon layer 20 and in third polysilicon layer 30. A sub-region of movable mass 22 implemented in second polysilicon layer 20 forms, with lower fixed electrode 12 located in first polysilicon layer 10 and upper fixed electrode 32 implemented in third polysilicon layer 30, a capacitor assemblage via gaps 13 and 23.
Specific design topologies for such assemblages are known, for example, from published German patent application document DE 10 2009 000 167 A1 for a Z acceleration sensor, and from published German patent application document DE 10 2009 000 345 A1 for a rotation sensor having detection deflections in a Z direction. The element of third polysilicon layer 30, alternatively to the function as an upper electrode, can also define a mechanical abutment that is preferably at the same electrical potential as the movable MEMS structure.
One problem with such MEMS structures can be the mechanical robustness of the mass element or electrode element implemented in second polysilicon layer 20 when the structure is deflected upward and abuts against the element, located thereabove, of third polysilicon layer 32. In particular when the plane of second polysilicon layer 20 is configured to be relatively thin, for example has a thickness from approx. 1 μm to approx. 3 μm, the risk of a mechanical breakage of the MEMS structure upon occurrence of a large overload (“drop test”) is quite high. The Z-abutment 81 implemented in cap wafer 80 is not effective when gap 23 between second polysilicon layer 20 and third polysilicon layer 30 is smaller than gap 61 between the upper side of third polysilicon layer 30 and the lower side of cap abutment 81.
Published German patent application document DE 10 2001 080 982 A1 has proposed, for example, in order to avoid breakage of the structure of second polysilicon layer 20, resiliently mounted structures of third polysilicon layer 30 which can absorb mechanical energy upon abutment and thereby limit the mechanical stresses on second polysilicon layer 20. The layout of these structures is complex, however, and requires additional space.
Also known, for example from U.S. Pat. No. 7,250,353B2, U.S. Pat. No. 7,442,570 B2, U.S. Patent Application Publications U.S. 2010 0109102 A1, U.S. 2011 0049652 A1, U.S. 2011 012247 A1, and U.S. 2012 0049299 A1, and published German patent application document DE 10 2007 048604 A1, are methods for vertical integration or hybrid integration or 3D integration in which at least one MEMS wafer and one evaluation ASIC wafer are mechanically and electrically connected to one another via wafer bonding methods.
Such vertical integration methods are particularly useful in combination with through silicon vias (TSVs) and flip chip technologies, with the result that construction and contacting can be accomplished as a chip-scale package, as known e.g. from U.S. Patent Application Publications U.S. 2012 0049299 A1 and U.S. 2012 0235251 A1.